JPH03200939A - Light wavelength converter - Google Patents

Abstract

PURPOSE:To maintain wavelength conversion efficiency and the incidence coupling efficiency of a fundamental wave high by charging an inert medium in a hermetically sealed container which houses a light wavelength converting element, and has a transparent window for transmitting the fundamental wave and a transparent window for transmitting a wavelength-converted wave. CONSTITUTION:The inert medium 21 is charged in the sealed container 20 which contains the light wavelength converting element 10, and has the transparent window 27 for transmitting the fundamental wave 15 and the transparent window 28 for transmitting the wavelength-converted wave 15''. Then when gas is used as the inert medium, the incident fundamental wave is prevented from shifting in convergence position owing to temperature variation and the wavelength-converted wave is prevented from being disabled to be converted in a small spot owing to the distortion of the wave front of the wavelength- converted wave. Consequently, the sublimation or variation of an organic nonlinear optical material can securely be precluded to prevent the fundamental wave from decreasing in incidence coupling efficiency, thereby maintaining the wavelength conversion efficiency of the light wavelength converting element high.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical wavelength conversion device that converts a fundamental wave into a second harmonic, a sum frequency, a difference frequency, etc. This invention relates to an optical wavelength conversion device that performs wavelength conversion using an optical wavelength conversion element using.

(Prior Art) Various attempts have been made to convert the wavelength of laser light into a second harmonic or the like (shorten the wavelength) using nonlinear optical materials. Specifically, as an optical wavelength conversion element that performs wavelength conversion in this way, for example, the one shown in "Fundamentals of Optoelectronics JA," written by YARIV, translated by Kunio Tada and Takeshi Kamiya (Maruzen Co., Ltd.), pages 200-204, is used. Bulk crystal type devices are well known. However, this optical wavelength conversion element uses the birefringence of the crystal to satisfy the phase matching condition, so even if the nonlinearity is large, it is possible to use a material with no or small birefringence. The problem was that the materials were not available.

As an optical wavelength conversion element that can solve the above problems,
A so-called fiber type has been proposed. This optical wavelength conversion element is an optical fiber whose cladding is filled with a core made of a nonlinear optical material, and is published in Journal of the Micro-Optics Research Group of the Japan Society of Applied Physics Vol. 3. N
(An example is shown in 12, p. 28-32. This fiber-type optical wavelength conversion element can easily achieve phase matching between the fundamental wave and the wavelength-converted wave. Research on fiber-type optical wavelength conversion elements has been actively conducted.Furthermore, as shown in Japanese Patent Laid-Open No. 63-15233 and No. 63-15234 by the present applicant, two cladding layers are used. A two-dimensional optical waveguide type optical wavelength conversion element is also known in which a slab-shaped leading waveguide made of a nonlinear optical material is formed between substrates.Furthermore, there is also a two-dimensional optical waveguide type optical wavelength conversion element in which a slab-shaped leading waveguide made of a nonlinear optical material is formed between substrates. A three-dimensional optical waveguide type optical wavelength conversion element in which a three-dimensional optical waveguide is embedded is also known.This leading waveguide type optical wavelength conversion element also has the above-mentioned features.

Incidentally, in recent years, various proposals have been made to use single-crystal organic nonlinear optical materials as the nonlinear optical material in these fiber type and guided waveguide type optical wavelength conversion elements.

Since this organic nonlinear optical material has an extremely large nonlinear optical constant compared to inorganic materials, it is possible to obtain high wavelength conversion efficiency by using this organic nonlinear optical material. Examples of this organic nonlinear optical material include those described in Japanese Patent Application Laid-open No. 60-250334 and "Nonllner
Optlcat properties of
Organic and PolymerlcM
material”AC8SYMPO8IUM 5E
RIES 223. Davld J, Will
aws edition (American Che@1cal 5o
ciety, 1983) "Organic Nonlinear Optical Materials" Supervised by Masao Kato and He Nakanishi (CMC Publishing Co., Ltd., 1983)
1985), “Non1lnear 0ptical
Propertiesof OrganicMo
lecules and crystals”D
, edited by S, Chesla and J, Zyss (Aca
demicPress Inc.

(published in 1987), The Quality and Perform by R.T., Balley et al.
ance or TheOrganle Non-L
lnear 0ptical Material(-
) 2-Ca-Methylbenzylas
lno) -5-N1tropYridine (M
BA-NP)' (Optics Cowmunl)
catlons, Vol. 65. No.J.
MNA (2-methyl-4
-nitroaniline), mNA (metanitroaniline), POM (3-methyl-4-nitroviridine-1-oxide), urea, NPP [N-(4-nitrophenyl)-(S)-prolinol], NPAN (2-[
N-(4-nitrophenyl)-N-methylaminocoacetonitrile), DAN (2-dimethylamino-5-
Nitroacetanilide), MBA-NP [2-N
(α-methylbenzylamino)-5-nitroviridine]
Furthermore, 3 shown in Japanese Unexamined Patent Publication No. 62-210432
, 5-dimethyl-1-(4-nitrophenyl)pyrazole, 3. 5-dimethyl-1-(4-nitrophenyl)
-1,2゜4-triazole, 2-ethyl-1-(4-
nitrophenyl)imidazole, 1-(4-nitrophenyl)pyrrole, 2-dimethylamino 1-5-nitroacetanilide, 5-nitro-2-pyrrolidinoacetanilide, 3-methyl-4-nitropyridine-N-oxide, etc. Can be mentioned. For example, MNA has a wavelength conversion efficiency about 2000 times higher than LiNbO3, which is an inorganic nonlinear optical material, so if an optical wavelength conversion element is formed using this organic nonlinear optical material, it can be used as a general small and low-cost device. It is also possible to obtain short wavelength laser light in the blue region by generating second harmonics and the like using the infrared laser light from the semiconductor laser as a fundamental wave.

(Problem to be Solved by the Invention) However, in a fiber type or optical waveguide type optical wavelength conversion element obtained by configuring the core of an optical fiber or a leading waveguide using the above-mentioned organic nonlinear optical material, conventionally, The problem has been recognized that wavelength conversion efficiency and fundamental wave incident coupling efficiency deteriorate significantly over time.

In other words, the organic nonlinear optical material constituting the optical wavelength conversion element comes into contact with the surrounding air or other atmosphere at its end face, so it sublimes from this part, shortening the single crystal part, or metamorphoses and ceases to be a single crystal. This results in the above-mentioned problem. In addition, in a three-dimensional optical waveguide type optical wavelength conversion element in which a guiding waveguide is embedded in the surface portion of a substrate, not only the end face but also the surface comes into contact with the surrounding atmosphere, so the above-mentioned problem occurs. more likely to occur.

Therefore, an object of the present invention is to provide an optical wavelength conversion device that can solve the above problems.

(Means and effects for solving the problem) The optical wavelength conversion device of the present invention includes a fiber type or guided waveguide type optical wavelength conversion element using the organic nonlinear optical material as described above, and a fundamental wave generating device. In an optical wavelength conversion device, the optical wavelength conversion device has a light source that transmits a fundamental wave and an input optical system that inputs a fundamental wave into an organic nonlinear optical material of an optical wavelength conversion element. It is characterized by being housed in an airtight container equipped with a transparent window and a transparent window that transmits the wavelength-converted wave emitted from the optical wavelength conversion element, and in which the airtight container is filled with an inert medium. be.

In the above configuration, the exposed portions of the organic nonlinear optical material, such as the end surfaces, come into contact with the inert medium, thereby preventing the above-mentioned sublimation and metamorphosis.

Even more preferably, the applicant's patent application No. 62-3
As disclosed in Japanese Patent No. 09145, a blocking layer is provided on the end surface of an organic nonlinear optical material to isolate this surface from an inert medium. Even if the organic nonlinear optical material is brought into contact with an inert medium as described above, the above-mentioned sublimation or metamorphosis may occur, although the progress is extremely slow compared to when it comes into contact with air or the like. However, if the above-mentioned blocking layer is provided, the end surfaces of the organic nonlinear optical material will not come into direct contact even with the inert medium, so that the above-mentioned sublimation or metamorphosis can be more reliably prevented. In addition, even if the barrier layer is made of organic resin, which has stability problems, the barrier layer is surrounded by an inert medium and deteriorates due to the atmosphere (for example, in the case of resin, it absorbs water vapor and deforms. This can prevent the physical properties of the resin from deteriorating due to oxidation or the like.

Note that it is conceivable to house the above-mentioned light source and incident optical system together with the optical wavelength conversion element in a closed container, and even in this case, the same effect as the present invention can be obtained in terms of protecting the organic nonlinear optical material. However, in that case, it is necessary to align the optical axes of the light source, the incident optical system, and the optical wavelength conversion element within a closed container, which makes this task difficult.

On the other hand, when assembling the optical wavelength conversion device of the present invention, once the optical wavelength conversion element is housed in an airtight container and filled with an inert medium, subsequent optical axis alignment is performed in this airtight container. Optical wavelength conversion element! Since it is only necessary to perform the adjustment, there is no need for the trouble of aligning the optical axis inside a closed container.

Although both liquid and gas can be used as the inert medium, it is more preferable to use gas. That is, inert liquids generally have a much greater temperature dependence of refractive index than inert gases.

Therefore, when this liquid is used, the focusing position of the fundamental wave focused by the input optical system changes depending on the ambient temperature, and the efficiency of incidence of the fundamental wave into the optical wavelength conversion element tends to decrease. Furthermore, the wavefront of the wavelength-converted wave that is emitted from the optical wavelength conversion element and passes through the inert liquid becomes easily distorted due to the change in the refractive index of this liquid, making it difficult to focus the wavelength-converted wave into a small spot. There is also.

On the other hand, if an inert gas whose refractive index is significantly less dependent on temperature than an inert liquid is used, the above-mentioned problems can be prevented.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an optical wavelength conversion device according to an embodiment of the present invention. This optical wavelength conversion device includes a closed container 20,
Fiber-type optical wavelength conversion element lO housed in it
, a semiconductor laser 18 that emits a fundamental wave 15 whose wavelength is converted by this optical wavelength conversion element 10, and a semiconductor laser 18 that emits a fundamental wave 15 whose wavelength is converted by this optical wavelength conversion element 10;
It has a collimator lens 17 and an objective lens 18 as an input optical system that allows the light to enter the core 11 of the optical wavelength conversion element 10.

The airtight container 20 is filled with fluorine-based oil 21, which is one of the inert media.

Note that the optical wavelength conversion element IO is held by a holding member 22 within the closed container 20. The airtight container 20 is also provided with a transparent window 27 that transmits the fundamental wave 15 and a transparent window 28 that transmits a second harmonic, which will be described later.

Next, the optical wavelength conversion element IO will be explained in detail.

As clearly shown in FIG. 2, this optical wavelength conversion element 10 is an optical fiber in which a core 11 made of a nonlinear optical material is filled in a hollow part at the center of a cladding 12. As the nonlinear optical material, an organic nonlinear optical material with high wavelength conversion efficiency is used as described above. In this example, in particular, the core 1 is
1 is formed.

Here, as an example, a method of manufacturing this optical wavelength conversion element IO will be described in the case where the core 11 is formed from the above-mentioned PRA and the cladding 12 is formed from 5FIO glass.

First, the hollow glass fiber 12” that becomes the cladding 12
will be prepared. As an example, this glass fiber 12° has an outer diameter of 1 mm and a hollow portion diameter of 1 μm. Then, as shown in Figure 3, PRAI
I' is kept in a molten state, and one end of a 12° glass fiber is immersed into this melt.

Then, due to capillarity, PRAII' in a molten state enters the hollow part of the glass fiber 12°.

Note that the temperature of the melt is slightly higher than the melting point (102° C.) of PRAII' in order to prevent decomposition of PRAII'. When the glass fiber 12° is then rapidly cooled, the P RA 11' that has entered the hollow portion becomes polycrystalline.

Next, the glass fiber 12' is gradually drawn out from the furnace maintained at a temperature higher than the melting point of PRAII' (for example, 102.5°C) to the outside of the furnace maintained at a temperature lower than the melting point, thereby changing the molten state. PRAII' is single-crystalized from the part drawn out of the furnace. As a result, an extremely long single-crystal core 11 with a uniform crystal orientation is formed, and the optical wavelength conversion element IO can be made sufficiently long. As is well known, the wavelength conversion efficiency of this type of optical wavelength conversion element is proportional to the length of the element, so the longer the optical wavelength conversion element is, the higher its practical value becomes.

After the core 11 is filled as described above, an acrylic resin such as an acrylic-styrene copolymer is applied to both end surfaces of the glass fiber 12'', which has been cut at both ends, to form a blocking layer 13aS13b. The formation of the blocking layers 13a and 13b is carried out, for example, by preparing a coating solution in which an acrylic resin is diluted with water, immersing both ends of the fiber in this solution, and then drying.

As a result, an optical wavelength conversion element IO as shown in FIGS. 1 and 2 is obtained. Note that the blocking layers 18a and 13b are formed to have a thickness of about 1 μm, for example.

The optical wavelength conversion element IO is used as shown in FIG. That is, the laser beam (fundamental wave) 15 with a wavelength of 890 nm, which is a diverging beam emitted from the semiconductor laser IB, is made into a parallel beam by the collimator lens 17, further condensed by the objective lens 18, and then passed through the transparent container 20. The light is transmitted through the window 27 and irradiated onto the element end face 10a through the blocking layer 13a.

This laser beam 15 converges on a small spot on the end face of the core 11 with the same diameter (1 μm in this example). Thereby, the laser beam 15 enters into the core 11. This fundamental wave 15 is converted by the PRA constituting the core 11 into a second harmonic wave having a wavelength of 1/2 at 15 degrees. This second harmonic wave of 15° is radiated into the cladding 12, undergoes repeated total reflection between its outer surfaces, and travels inside the element 10 toward the end face side. Phase matching is achieved between the guided mode of the fundamental wave 15 in the core and the radiation mode of the second harmonic 15° to the cladding (in the case of so-called Cerenkov radiation).

From the output end face 10b of the optical wavelength conversion element IO, the second
A beam 15" containing harmonics of 15° is emitted. This emitted beam 15" is emitted outside the container through the transparent window 2B of the sealed container 20, is made into a parallel beam by the collimator lens 30, and is condensed by the condenser lens 31. be illuminated. At this time, the output beam 15'' is passed through the filter 32, and the second harmonic 15'' is passed through the filter 32.
Only 5° is taken out.

In order to assemble the optical wavelength conversion device as described above, it is necessary to align the optical axes of each element. Once filled, it is possible to align the optical axis by adjusting the position of the optical wavelength conversion element IO in the sealed container 20. In other words, in this device, the closed container 2
There is no need to worry about the trouble that would occur if the optical wavelength conversion elements 1OO40 were also housed in the container 20 and their optical axes were aligned in the sealed container 20.

In this device, since the optical wavelength conversion element 1O is confined in the fluorine-based oil 21, which is an inert medium, the end face of the core 11 made of PRA, an organic material, does not come into contact with the atmosphere such as air. Therefore, sublimation and metamorphosis of this core 11 are prevented. Moreover, in this embodiment, since the blocking layers 13a and 13b are provided on both end faces of the optical wavelength conversion element IO, the end faces of the core 11 do not even come into contact with the fluorine-based oil 21, so that the above-mentioned sublimation and metamorphosis are more reliable. is prevented.

Note that if the blocking layer 18aS13b is provided, the preferable results as described above can be obtained, but such a blocking layer does not necessarily have to be provided.

Furthermore, in the above embodiment, the fluorine-based oil 21 is used as the inert medium filled in the closed container 20.
Other examples of this inert medium include silicone oil, liquid paraffin for liquids, N2 SHe, N2 for gases, etc.
es Ar, Kr, Xe, etc. can be used. Furthermore, in the above embodiment, acrylic resin is used as the material for the barrier layers 13a and 13b;
In addition, examples of materials 3a and 13b include silicone resin, epoxy resin, fluororesin, gelatin, casein, collagen, cellulose, polyvinyl alcohol, polyvinyl acetate, polyethylene terephthalate,
Polyurethane, unsaturated polyester, phenol, polyamide, alkyd resin, etc. can be used.

FIG. 4 shows another embodiment of the invention using an inert gas as described above. Note that in FIG. 4, elements equivalent to those in FIG. 1 are given the same numbers, and detailed explanations thereof will be omitted.

In the apparatus shown in FIG. 4, a closed container 20 is filled with dry hh (nitrogen) gas 50, which is one of the inert gases. Of course, other gases mentioned above can also be used instead of this N2 gas 50. This filling with N2 gas 50 can be carried out by, for example, providing a gas inlet and a gas outlet (not shown) in the closed container 20, and replacing the air inside the closed container 20 with the N2 gas 50 fed from the gas inlet. This can be done by then closing the gas inlet and outlet. Furthermore, filling with N2 gas 50 can also be achieved by assembling the sealed container 20 in the camber 1 or glove box that has been replaced with this gas 50. In this case, it is necessary to provide a gas inlet and an outlet in the sealed container 20. There is no.

In this example as well, 50 ml of N2 gas as an inert medium is used.
By filling the airtight container 20 with the core 11, sublimation and metamorphosis of the core 11 are prevented.

Furthermore, in this embodiment, since a gas whose refractive index is less dependent on temperature than an inert liquid is used as the inert medium, the convergence position of the fundamental wave 15 focused by the objective lens 18 depends on the temperature. Furthermore, the wavefront of the second harmonic 15° emitted from the optical wavelength conversion element 10 is distorted.
The problem that it becomes difficult to focus the light into a small spot using the condensing lens 31 is unlikely to occur. Therefore, in this device, there is no need to readjust the optical system in response to changes in ambient temperature.

In addition, especially in the apparatus shown in FIG. 4, an oxygen scavenger 51. A dehydrating agent 52 and an adsorbent 53 are fixed. These oxygen scavengers51. When the dehydrating agent 52 and adsorbent 53 are stored in the closed container 20, N2 gas 5
0, or active gases such as moisture, solvents, and oxygen that have evaporated from the resins constituting the blocking layers 13a and tabs, and further exist as impurities in the gas used for the replacement. Moisture, oxygen, and other active gases adhering to the inner wall of the sealed container 20 are removed by the optical wavelength conversion element lO.
can be removed from the atmosphere. If so, if the blocking layer 13aS13b is made of resin, it may deteriorate due to oxidation, or the blocking layer 18aS18 may deteriorate.
When b is made of a natural or semi-synthetic polymer compound such as gelatin, casein, collagen, or cellulose, it is possible to prevent problems such as mold growth on them.

In order to obtain the above-mentioned effects, the oxygen scavenger 51. Although it is most preferable to store all of the dehydrating agent 52 and adsorbent 53 in the closed container 20, a certain effect can be obtained even if one or two of them are stored.

As the above-mentioned oxygen absorber 51, for example, an iron-based oxygen absorber, an oxygen absorber using activated carbon and ortho-di-phenol, etc. can be used. Examples of the dehydrating agent 52 include activated alumina, molecular sieve (crystalline zeolite), silica gel, Pz 05 , Mg(ClO4)2, Ba0
SKOH, NaOH, Cao, CaSO4, Mg0SC
aC12 etc. can be used. Further, as the adsorbent 53, for example, activated alumina, molecular sieve, silica gel, etc. can be used.

Note that in the above two embodiments, a fiber type optical wavelength conversion element IO is used, but the optical wavelength conversion device of the present invention
Of course, it is also possible to construct the optical wavelength conversion element using the two-dimensional or three-dimensional optical waveguide type described above.

Further, although the above embodiment converts the fundamental wave into a second harmonic, the optical wavelength conversion device of the present invention may also use an optical wavelength conversion element that converts the fundamental wave into a sum frequency, a difference frequency, etc. It can also be configured as follows.

(Effects of the Invention) As explained in detail above, the optical wavelength conversion device of the present invention has a configuration in which the optical wavelength conversion element that performs wavelength conversion using an organic nonlinear optical material is confined in an inert medium. Sublimation or metamorphosis of the material is reliably prevented. Therefore, according to this optical wavelength conversion device, it is possible to prevent the incident coupling efficiency of the fundamental wave from decreasing and maintain a high wavelength conversion efficiency of the optical wavelength conversion element.

Furthermore, by adopting the above configuration, it is possible to prevent dust from adhering to the end face of the optical wavelength conversion element or from being scratched, and from this point, it is also possible to prevent the wavelength conversion efficiency of the optical wavelength conversion element from decreasing. Furthermore, the effect of improved handling properties can also be obtained.

Furthermore, in the optical wavelength conversion device of the present invention, there is no need to align the optical axes of the optical wavelength conversion element and other optical elements within a sealed container, so that the optical wavelength conversion device of the present invention does not require optical axis alignment between the optical wavelength conversion element and other optical elements. Damage to the end face of the wavelength conversion element and deterioration of the organic nonlinear optical material from the end face portion can be reliably prevented.

Furthermore, when gas is used as an inert medium, it is possible to prevent the focusing position of the incident fundamental wave from changing due to temperature changes and the wavefront of the wavelength-converted wave from being distorted, making it impossible to narrow it down to a small spot. There is no need to readjust the optical system depending on the temperature.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view showing an optical wavelength conversion device according to an embodiment of the present invention, FIG. 2 is a perspective view showing an optical wavelength conversion element used in the device of the above embodiment, and FIG. 4 is a schematic diagram illustrating a method of manufacturing the optical wavelength conversion element, and FIG. 4 is a partially cutaway side view showing an optical wavelength conversion device according to another embodiment of the present invention. lO... Optical wavelength conversion element 11... Core 12...
・Clad 13a% 18b...Barrier layer 15
... Fundamental wave 15° ... Second harmonic 1B
...Semiconductor laser 17.30...Collimator lens 18...Objective lens 20...Airtight container 21
...Fluorine oil 27.28...Transparent window 31
...Condensing lens 50...N2 gas 51...
・Oxygen scavenger 52...Dehydrating agent 53...Adsorbent No. 2 Figure 0 Figure 6゜Drawing subject to correction May 9, 2000 7゜Contents of correction (1) Box 1 and Figure 1 in the drawing Figure 4 is corrected as attached. 2000 Patent Application No. 063.731 2゜Name of the inventionRelationship with the person who makes the light wave conversion and purchase amendmentWrf ApplicantAddress 210 Nakazake, Minamiashigara City, Kanagawa PrefectureName +520) Agent for Fuji Photo Film Co., Ltd. Address: 5-2 Roppongi, Minato-ku, Tokyo 7th floor, Hauraiya Building Voluntary? III positive

Claims (2)

[Claims] (1) an optical wavelength conversion element formed by covering an organic nonlinear optical material with a cladding layer having a lower refractive index than the organic nonlinear optical material, converting the wavelength of an incident fundamental wave and emitting it; and a light source generating the fundamental wave; an entrance optical system that makes the fundamental wave enter the organic nonlinear optical material of the optical wavelength conversion element; a transparent window that houses the optical wavelength conversion element and that transmits the fundamental wave output from the input optical system; An optical wavelength conversion device comprising an airtight container equipped with a transparent window that transmits wavelength-converted waves emitted from a conversion element, and an inert medium filled in the airtight container. (2) The light wavelength according to claim 1, wherein the inert medium is an inert gas, and at least one of an oxygen scavenger, a dehydrating agent, and an adsorbent is contained in the closed container. conversion device.